<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <style>
    body {
      text-align: center;
    }
    button {
      white-space: nowrap;
      margin-bottom: 10px;
    }
  </style>
</head>
<body>
  <button id="on">变灰</button>
  <button id="off">取消</button>

  <script src="popup.js"></script>
</body>
</html>